If I understand your wanting to be able to do is switch between the SDR-Play and a amateur radio transceiver based transmitter ?.

Normally in a transceiver the receiver and transmitter stages are switched using a relay (Often solid state, but can be mechanical). The relay switches the antenna from its normal position were the antenna is connected to the receiver to the transmitter stage when the microphone key switch is pressed, at the same time the transmitter is activated and the receiver input via the relay is either shunted to ground via a resistor or directly to ground. This protects the front end of the receiver from being exposed to the high power of the transmitter.

If using the same antenna for reception and transmission then you need to switch the antenna between the SDR-Play and transmitter on your transceiver and to do this you will need to use a relay. Coaxial based relays with 12volt coils can be found on ebay second hand for a reasonable quality unit and have your microphone switch the transmitter on and run the relay at the same time. Prices of RF relays vary depending on complexity, age and power handling which for most radio amateurs is not much.

If your using the SDR for this purpose then you don't need to worry over what the SDR is doing so long as it is isolated from the transmitter when the Tx is operating. No need to worry over turning off the audio from it unless you write software or find some software which allows the audio to be turned off when the key to transmit switch is pressed.

I'm a bit unclear as to what you want to accomplish. Is the goal to use the SDRplay as a panadapter to your transceiver? If so, we would need to know more info regarding the transceiver, software to be used, etc.

I've configured the SDRplay as an external panadapter with my TS-590S and another with my TS-990S. The primary SDR software application is SDR-Radio Console although from time-to-time I use HDSDR. Both work great with SDRplay.

I also use Ham Radio Deluxe and have been able to "integrate" HRD, SDR-Radio the Transceiver and SDRplay for point-and-click tuning of the displayed spectrum or waterfall. This is accomplished by using a virtual com port SPLITTER from Eterlogic (their VSPE can be configured as a splitter).

As for the DXE-RG-5000, I used this RF limiter for about a year just as incremental protection. The problem is when the RG-5000 is used with a "longer wire" antenna such my 80m OCF dipole it introduces considerable intermod products. At first I thought this was an issue with my SDRs (SDRplay, Afedri SDR-Net and SDR-IQ). However, when I removed the RG-5000 from the "circuit" the intermod disappeared. Contacts with several other hams discovered they too had major intermod issues with their RG-5000s, so I'm led to believe this is a major design problem with the RG-5000 (or it was never intended for this application).